I cannot personally speak on the performance of the aluminum pro, other than using one of my friend's once or twice. However, I have the black macbook (late 2008 i think? shipped with Leopard). Anyway, it has 4 GB of ram, 150 GB hard drive, and it's a 2.2 GHz core 2 duo.

Just with my experience with various computers, i don't think the 0.27 GHz will show much speed difference. I run photoshop, final cut pro, etc. pretty often on this machine. Also, I boot-camped windows xp on my macbook last semester AND ran AutoCAD 2010 on it.

Having that said, I think you can save the $600 and do just fine. Keep in mind, I'm not sure what you will be using it for exactly since you mentioned your school upping the specs.